1. Technical Field
The present invention relates to technology for detecting image blur.
2. Related Art
In recent years, digital still cameras have become widespread, and the capacity of the memory cards used for these has also increased. Because of this, the opportunity for general users to shoot large volumes of images has increased. With digital still cameras, there is no need to change film, and since shooting is performed easily, there is a good deal of shooting images without being conscious of subject shaking or hand shaking. Therefore, when trying to print the shot images on a printer, there are a relatively large number of images for which blurring has occurred with the image due to subject shaking or hand shaking, and it was necessary to do the work of selecting proper images ahead of time.
The work of selecting proper images from among a large volume of images is a very troublesome task. In light of this, to handle this kind of problem, there is a desire for technology that automatically eliminates from the printing subjects the images for which blur has occurred before the user prints the images. Regarding this kind of blur detection technology, noted in JP-A-4-170872 is a technology that determines the sharpness (in other words, the level of blurriness) of images for each block by performing a frequency analysis for each block that has undergone discrete cosine transform after the shot image is divided into a plurality of blocks with units of 8 pixels×8 pixels (as technology related to this application, also see JA-A-10-271516 and JP-A-2002-51178).
However, the resolution of images shot using the digital still cameras of recent years is high resolution of from several million to tens of millions of pixels, so it was difficult to determine the blur or sharpness within just a block constituted by 8 pixels×8 pixels as noted in JP-A-4-170872. To put this in specific terms, when printing an image of 6,000,000 pixels (approximately horizontal 3000 pixels×vertical 2000 pixels) on an L size printing paper (approximately horizontal 130 mm×vertical 90 mm), a width of the block nearly equivalent to 0.35 mm, and within this kind of narrow width, it is difficult to objectively determine whether an image is sharp or blurry. In other words, with the high resolution images shot in recent years, directly applying the technology noted in JP-A-4-170872 is difficult.
Also, when trying to analyze the blur of high resolution images of several million pixels or greater using the technology noted in JP-A-4-170872, the calculation volume is huge, and along with this, a large volume of memory is used. This kind of problem is a problem that particularly cannot be overlooked when performing blur detection with compact devices which have limits in terms of CPU power and memory capacity such as printers, digital cameras, photo viewers, and the like.